Gas or liquid filter

ABSTRACT

A gas or liquid filter structure comprising a fibrous filter web arranged in alternating folds and in which there is positioned between adjacent folds a grid-like distance member which presents a portion adapted to conform to the contours of each fold edge and support it from within.

United StatesPatent Hagdahl [451 Apr. 11, 1972 [54] GAS 0R LIQUID FILTER[56] References Cited [72] Inventor: Erik Lennart Hagdahl, Bergsatra,Sweden UNITED STATES PATENTS [73] Assignee: Stora Kopparbergs BergslagsAktiebolag, 930,561 8/1909 Rahe ..55/500 X F l Sw d 2,681,155 6/1954Graham ..210/493 3,410,062 11 1968 Hart [22] Filed: Mar. 3, 1970 55,521

[21 Appl. No.: 16,126 FOREIGN PATENTS OR APPLICATIONS 1,022,232 3/ 1966Great Britain ..55/521 [30] Fouls" Application Pmmy Dam v PrimaryExaminer-Reuben Friedman .s, 1969 s 'd ..3050 69 I Assistant Granger Marwe en Attorney-Stevens, Davis, Miller & Mosher [52] 0.8. CI ..210/493,55/500, 55550550291, [57] ABSTRACT I [51 Int. Cl. ..B0ld 29/06 A gas orliquid filter structure comprising a fibrous filter web [58] Field 01Search ..210/227, 228, 230, 231, 483, arranged in alternating folds andin which there is positioned between adjacent folds a grid-like distancemember which presents a portion adapted to conform to the contours ofeach fold edge and support it from within.

'7 Claims, 7 Drawing Figures PATENTEUAPR 11 I972 3,655,060

SHEET 2 [IF 2 The present invention relates to a filter or gas andliquid media, including a filter means in the form of a web of fibrousmaterial which has been folded transversely of its longitudinalextension, to form a plurality of substantially equally sized filtersurfaces which extend generally parallel to each other and which aredefined by parallel fold edges alternating towards the inlet and outletside of thefilter and which are FIG. 5 shows a section taken through theline V-V in FIG. 4.

FIG. 6 shows a section taken through line Vl-VI in FIG. 4.

FIG. 7 shows in larger scale a partial section of a modification of thefilter of FIGS. 4-6, similar to FIG. 5.

As is seen from FIGS. 1-7, where corresponding parts are identified withthe same reference numerals, the filter of the present inventioncomprises a filter means in the form of a fibre material web 1 which isfolded transversely of its longituheld apart y distance means mountedbetween adlawm filter dinal extension, to form a plurality ofsubstantially equal size surfaces.

As a result of their large total filter area, filters of this type canbe given a very high capacity and, among other things, are suitable forfiltering gases, for example air, particularly when it is necessary toobtain large quantities of filtered gas in a short period of time andwhen it is desirable to obtain the least possible pressure drop acrossthe filter. Such filters are used, for example, when producing sterileor particle-free air for socalled clean rooms, which are used within thepharmaceutical industry and in the precision-tool industry and otherfields where it is necessary to work in a particle-free atmosphere. Thefiltering agent primarily used in such filter means is glass fibrepaper, which, despite imparting to the gas or liquid flowingtherethrough a very high degree of purity, gives rise to but arelatively small drop in pressure.

The previous manufacture of filters of the type described oftenincorporate the use of thin, corrugated aluminium plates as distancepieces, the corrugation folds being arranged to extend in thelongitudinal direction of the fibre material web, i.e. substantially atright angles to the fold edges, so that the medium being filteredobtains through the corrugating folds free passage towards and away fromrespective filter surfaces. The corrugated aluminium plates, however,often cause damage to the fibre material web and, furthermore, offer butslight support to the fold edges. It has also been suggested to use.

distance means made of corrugated cardboard. These distance means,however, gave but a small degree of rigidity to the filter and, similarto the corrugated aluminium plates, offer but small support to the foldedges. The object of the present invention is to provide a novel andconvenient filter of the type described, in which the fibre material weband its fold edges are gently but effectively supported and protectedagainst external damage.

For the purpose of achieving this object, it is suggested in accordancewith the invention that the distance means each 7 include two edgepieces extending transversely of the longitudinal direction of the fibrematerial web and situated at the inlet and outlet side of the filter,and stiffening means which join the opposing inner edges of the edgepieces and which hold their adjacent filter surfaces in spacedrelationship in a manner to form between the inner edges of the edgepieces passages which are open towards the adjacent filter surfaces,wherewith one edge piece supports from within with its outer edge thefold edge common the filter surfaces held apart by the distance means,while the other edge piece is so situated and constructed that, betweenthe inner edge thereof and the two fold edges situated adjacent saidedge piece and defining the two filter surfaces held apart by thedistance means, there is formed a slot which permits the medium beingfiltered to flow towards and away from the passages, and in that theouter edge surface of said other edge piece is situated outside the twolast-mentioned fold edges to protect said edges against external damage.

The invention will now be described in detail with reference to a numberof embodiments illustrated in the accompanying drawings.

FIG. 1 is a perspective view of a first embodiment of a filter accordingto the invention.

FIG. 2 shows in larger scale a partial cross sectional view of thefilter according to FIG. 1.

FIG. 3 shows in side projection one of the distance pieces used in thefilter illustrated in FIG. 1 and 2.

FIG. 4 shows in vertical projection a second embodiment of the filter ofthe invention.

filter surfaces which extend generally parallel with each other andwhich are defined by parallel fold edges arranged to alternate towardsthe inlet and outlet side of the filter, and which filter surfaces areheld apart by distance pieces 2 mounted between adjacent filtersurfaces.

Only a portion of the fibre material web 1 and a few of the distancepieces embodied therein have shown in FIG. 1. The full extension of thefilter is shown by the morse lines. As will be seen from FIGS. 1-3, eachdistance piece 2 comprises two edge pieces 3, 4 situated at the inletand outlet side of the filter and extending transversely of thelongitudinal extension of the fiber material web 1, and stiffening means10, ll, 12 and 13 which join the opposing inner edges 5 and 6 of theedge pieces and hold apart the filter surfaces engaging said stiffeningmeans in a manner whereby passages 7, 8 and 9 which open towards theadjacent filter surfaces are formed between the inner edges 5, 6 of theedge pieces. One edge piece 3 of each distance means 2 supports fromwithin the fold edge 15 com mon the two filter surfaces held apart bythe distance piece, while the other edge piece 4 is so situated andconstructed that between its inner edge 6 and two fold edges situatedadjacent the edge piece 4 are provided slots 14 for permitting themedium being filtered to flow towards arid away from the passages 7, 8and 9. The outer edge surface of each edge piece 4 is situated outsidethe fold edges 15 adjacent this edge piece, so that a grid structurewhich protects the fold edges 15 against external damage is formed onboth the inlet side and the outlet side of the filter, as is clearlyevident from FIGS. 1 and 2.

With the filter illustrated in FIGS. 1-3, the distance pieces 2 presentfiat surfaces for abutment with adjacent filter surfaces. The distancepieces 2 have the form of open grid structures and can have beenproduced by punching the areas forming the passages 7, 8, 9 from flatplate. The thus integrally formed distance pieces may suitably comprisea non-corrosive material, for example a semi-hard or hard plasticmaterial, and may, in at least certain areas, be secured by an adhesiveto adjacent filter surfaces, to increase the strength of the filter andoptionally render the same self-supporting to such an extent that it canbe used without embodying an external strengthening frame surroundingthe filter, or other support means.

The inner edges 6 of the edge pieces 4 are so constructed, for examplerounded or chamfered, that they provide and form guides for asubstantially laminar noiseless fiow of the medium being filtered, outof and into the filter.

As will be seen from FIG. 1, each stiffening rib 10, 11, 12 or 13 of thedistance piece 2 may be situated opposite a stiffening rib of each ofthe remaining distance pieces 2, whereby a pillar-like structure isformed transversely of the through-flow direction of the filter, whichimparts a high degree of strength to the filter. Furthermore, as isshown in FIG. 1, each distance piece may present two stiffening ribs 10and 13 extending along and opposite their respective one of the longedges of the folded fibre material web 1, whereby the long edges of thefibre web are effectively protected and two stable filter sides areformed, at which means can be mounted for securing the filter in afilter box.

The simplest manner of producing the slots 14 in the embodimentillustrated in FIGS. 1-3 is to arrange that the distance between theouter edge of the edge piece 3 and the inner edge 6 of the edge piece 4at each distance piece 2 slightly exceeds the extension of each filtersurface 17 the lon- 5 gitudinal direction of the fibre material web 1.

When producing the filter illustrated in FIGS. 1-3, a distance piece 2is placed over an unfolded fibre material web 1 with the edge pieces 3and 4 of the distance piece arranged transversely of the longitudinaldirection of the web, whereafter the web 1 is folded over the distancepiece 2 parallel with itself. Another distance piece 2 is then placedover the fibre web and the preceding distance piece, although slightlyoffset in relation thereto, so to form a slot 14 between the fold edgeformed when the web 1 is folded over the inner edge piece 3 of thelatter distance piece and the inner edge 6 of the edge piece 4 of thefirst distance piece.

The distance pieces 2 are then subsequently placed in position,alternately offset to the same extent as the two distance pieces firstmounted, and in this way slots 14 are obtained between the fold edges 15and the outer edge pieces 4 of the distance pieces 2. The surfaces withwhich the distance pieces 2 abut the fibre material web are suitablycoated with an adhesive, before the distance pieces are placed on theweb 1 and the web folded over the edge pieces 3.

It is also possible, however, to use a fibre material web 1 which hasbeen prefolded to the illustrated shape, and to introduce distancepieces 2 in the folds alternately from different directions.

FIGS. 4-6 illustrate a filter constructed in accordance with theinvention and in which practically the whole of the surface of the fibrematerial web is used for filtering purposes. This filter is, in itsentirety, less durable than the filter of the embodiment illustrated inFIGS. 1-3, but the advantages gained with the widely increased activefilter surface are often so great that they outway its disadvantages,which may include the necessity of stiffening the filter with a suitableexternal frame before it can be placed in operation. The filterillustrated in FIGS. 4-6 is particularly suitable when the lowestpossible noise effect is desired at the filter and when, owing toshortage of space, for example, it is not possible to increase thenumber of filter folds. The noise level of a filter is, to a largeextent, a result of its resistance to through-flow, and the easiest wayof reducing this resistance is to increase the active filtering surfaceof the filter. In the case of a filter with which it is desired tomaintain a low noise level, it is generally necessary, furthermore, tobe satisfied with a relatively low throughflow speed, since this factoralso plays a large role in the noise level of the filter, and hence awide filter surface is required.

In the exemplary embodiment of the filter of FIGS. 4-6, each distancepiece 2 comprises two parallel edge pieces 16 and 17, which extendtransversely of the longitudinal direction of the fibre material web 1and are joined by means of stiffening ribs 21 extending between saidedge pieces. The distance between the outer edge surfaces of the edgepieces 16, 17 exceeds the length of each filter surface in thelongitudinal direction of the filter material web 1, and hence the outeredge surface of the outer edge piece 16 of each distance piece 2 at theinlet and outlet side of the filter is located outside a plane passingthrough the fold edges 19 on the inlet and outlet side and protects thefold edges 19 against external damage, while the opposite, inner edgepiece 17 of each distance piece 2 supports with its outer edge surface18 from within the common fold edge 19 for the filter surfaces heldapart by the distance piece in question. Arranged between the inner edgesurface 20 of each outer edge piece 16 and the fold edges 19 situatedadjacent this edge piece are slots 14, which permit the medium beingfiltered to pass into and out of a number of passages 22, which are opentowards the adjacent filter surfaces and positioned adjacent thestiffening ribs 21.

The stiffening ribs 21 abut the filter surfaces along only nar row edgesurfaces, said stiffening ribs obtaining their necessary inherentrigidity by having a certain extension parallel with the filter surfacesat a distance therefrom. Thus, the stiffening ribs 21 present arectangular cross section, so oriented that one diagonal thereof isessentially perpendicular to the filter surfaces and the other diagonalsubstantially parallel with said surfaces. The stiffening ribs 21 thuspresent a corner edge to each of the filter surfaces, whereupon asubstantially line abutment is obtained. The edge pieces 16 and 17 havebeen given the same rectangular cross section, and in this way anadvantageous support to the fold edges 19 of the filter fold is obtainedat the same time as the outer edge pieces 16 obtain an aerodynamically,or hydrodynamically advantageous shape for guiding the medium undergoingfiltration into and out of the filter.

As will be seen from FIG. 7, the slots 14 between the outer edge pieces16 and the filter folds l9 situated adjacent said edge pieces can beobtained even though the outer edge pieces are not placed in theirentirety outside a plane which passes through the filter folds 19 of theinlet side and the outlet side of the filter.

It naturally lies within the scope of the invention to use, with regardto the edge pieces and stiffening ribs of the distance pieces, crosssectional shapes, other than those shown. Thus, another suitable crosssectional profile of the stiffening ribs of the distance pieces and alsoof the edge pieces in the embodiment illustrated in FIGS. 4-7 is atriangular one, and it should be understood that many other profiles arealso suitable in the present connection. The different components of thedistance pieces may also be given mutually different cross sectionalprofiles and subsequently different forms of abutment with the filtersurfaces. In connection herewith, for the purpose of stiffening thefilter the stiffening ribs may be given shapes of such mutually varyingform that abutment edges for a line abutment effect are alternated withwider abutment surfaces. When desiring to obtain a line abutment effect,it must be ensured that the filter surfaces are not damaged by thenarrow abutment edges. A suitable selection of the material for thedistance pieces is then very important, and among those materialssuitable can be mentioned semi-hard plastics, The arrangement of theinvention is not restricted to the modifications illustrated in thedrawing, but can be varied within the scope of the following claims.

What is claimed is:

1. A filter for gaseous and liquid media, comprising in combination afilter means in the form of a web of fibrous material foldedtransversely of its length to form a plurality of substantially equalsized filter surfaces, which extend generally parallel to one anotherand which are defined by parallel folds alternating towards the inletand the outlet side of the filter and are held apart by filter surfacespacing means, wherein each of the spacing means has the form of an opengrid-like structure, comprising two edge pieces extending transverselyof the longitudinal direction of the web of fibrous material and locatedat the inlet and the outlet side of the filter, and stiffening ribs,which join the edge pieces together at their respective opposing inneredge surfaces said edge pieces and said stiffening ribs beingsubstantially coplanar, and which stiffening ribs are positioned alongsaid edge pieces in a manner such that each stiffening rib of onespacing means is located opposite a corresponding stiffening rib of theremaining spacing means in the filter, whereby said stiffening ribs,together with intermediate filter material, form reinforcing columns,which extend along the whole filter, and wherein one edge piece of eachspacing means supports from within at its outer edge surface the foldcommon to the two filter surfaces held apart by means, while the otheredge piece of the same spacer means is located and formed in a manner toprovide between the inner edge surface of said other edge piece and thetwo folds situated adjacent thereto and defining the filter surfacesheld apart by the spacer means, a gap which permits flow of the mediumbeing filtered to and from said surfaces, and wherein said other edgepiece is arranged to protrude beyond the two last mentioned folds toprotect the same from physical damage.

2. A filter according to claim 1, wherein the distance in each spacingmeans between the outer edge surface of said one edge piece and theinner edge surface of said other edge piece slightly exceeds theextension of each filter surface in the longitudinal direction of theweb of fibrous material.

3. A filter according to claim 1, wherein each spacing means is providedwith two stiffening ribs, which extend opposite each other between saidedge pieces and along the long edge of the folded web of fibrousmaterial.

4. A filter according to claim 1, wherein each spacing means is a singleintegral unit.

5. A filter according to claim 1, wherein the said other edge piece ofeach spacing means has a shape which comprises means for allowingsubstantially laminar flow of the medium being filtered into and fromthe filter.

6. A filter according to claim 1, wherein at least one of the stifieningribs is constructed so that it abuts the adjacent filter surfaces alonga narrow edge surface, the width of which comprises only a portion ofthe largest width of the stiffening ribs in the direction across theplane of the fibrous material web.

7. A filter according to claim 6, wherein the stiffening rib presentinga narrow abutment edge surface comprises a member having aparallelogram-shaped cross-sectional area, the one diagonal of whichextends between the adjacent filter surfaces while the other diagonalextends substantially parallel with said filter surfaces.

1. A filter for gaseous and liquid media, comprising in combination afilter means in the form of a web of fibrous material foldedtransverSely of its length to form a plurality of substantially equalsized filter surfaces, which extend generally parallel to one anotherand which are defined by parallel folds alternating towards the inletand the outlet side of the filter and are held apart by filter surfacespacing means, wherein each of the spacing means has the form of an opengrid-like structure, comprising two edge pieces extending transverselyof the longitudinal direction of the web of fibrous material and locatedat the inlet and the outlet side of the filter, and stiffening ribs,which join the edge pieces together at their respective opposing inneredge surfaces said edge pieces and said stiffening ribs beingsubstantially coplanar, and which stiffening ribs are positioned alongsaid edge pieces in a manner such that each stiffening rib of onespacing means is located opposite a corresponding stiffening rib of theremaining spacing means in the filter, whereby said stiffening ribs,together with intermediate filter material, form reinforcing columns,which extend along the whole filter, and wherein one edge piece of eachspacing means supports from within at its outer edge surface the foldcommon to the two filter surfaces held apart by means, while the otheredge piece of the same spacer means is located and formed in a manner toprovide between the inner edge surface of said other edge piece and thetwo folds situated adjacent thereto and defining the filter surfacesheld apart by the spacer means, a gap which permits flow of the mediumbeing filtered to and from said surfaces, and wherein said other edgepiece is arranged to protrude beyond the two last mentioned folds toprotect the same from physical damage.
 2. A filter according to claim 1,wherein the distance in each spacing means between the outer edgesurface of said one edge piece and the inner edge surface of said otheredge piece slightly exceeds the extension of each filter surface in thelongitudinal direction of the web of fibrous material.
 3. A filteraccording to claim 1, wherein each spacing means is provided with twostiffening ribs, which extend opposite each other between said edgepieces and along the long edge of the folded web of fibrous material. 4.A filter according to claim 1, wherein each spacing means is a singleintegral unit.
 5. A filter according to claim 1, wherein the said otheredge piece of each spacing means has a shape which comprises means forallowing substantially laminar flow of the medium being filtered intoand from the filter.
 6. A filter according to claim 1, wherein at leastone of the stiffening ribs is constructed so that it abuts the adjacentfilter surfaces along a narrow edge surface, the width of whichcomprises only a portion of the largest width of the stiffening ribs inthe direction across the plane of the fibrous material web.
 7. A filteraccording to claim 6, wherein the stiffening rib presenting a narrowabutment edge surface comprises a member having a parallelogram-shapedcross-sectional area, the one diagonal of which extends between theadjacent filter surfaces while the other diagonal extends substantiallyparallel with said filter surfaces.